A conventional height adjustable device for overbed table is disclosed in U.S. Pat. No. 5,775,234 and 4,715,295, and generally includes a hydraulic cylinder received in the retractable tube assembly so as to adjust the height of the inner tube relative to the outer tube. Nevertheless, when adjusting the table by using the hydraulic cylinder, the user has to unlock the cylinder by one hand and press the table by the other hand. This is difficult for a shorter user who needs to stand up at toes and to try to bend his or her arm to press the table downward. Besides, the hydraulic cylinder potentially has a problem of leakage and the maintenance cost is high for an overbed table.
The present invention intends to provide a height adjustable device that is easily to be operated by operating a lever which drives a cable to pull the device in the inner tube so as to unlock the device and the inner tube can be freely moved in the outer tube.